1. Field of the Invention
The present invention relates to a variable delivery fuel supply device, which is used for an internal combustion engine, particularly for a cylinder injection type gasoline engine requiring a high pressure fuel, and controls a supply quantity of a fuel, supplied to a fuel injection valve.
2. Discussion of Background
A variable delivery fuel supply device used in a combustion engine for automobiles is constructed by a plurality of fuel injection valves supplying a fuel into cylinders of the combustion engine, a delivery pipe supplying the fuel to these fuel injection valves, a fuel pump supplying the fuel to the delivery pipe after pressurizing the fuel, a low pressure pump supplying the fuel from a fuel tank to the fuel pump, a control means controlling a time of injecting the fuel, an amount of injecting the fuel, a discharge quantity from the fuel pump and so on, and so on. The fuel pump is constructed by a cylinder, a plunger, which is driven by a driving cam, is located in a camshaft of the internal combustion engine, and intakes the fuel into a pressurization chamber in an intake stroke and sends the fuel inside the pressurization chamber to the delivery pipe with pressure in a discharge stroke by reciprocal movements inside the cylinder, and an electromagnetic valve controlling the discharge quantity from the pressurization chamber by relieving the pressurized fuel inside the pressurization chamber at predetermined timing and also controlling a pressure of the fuel in the delivery pipe to be a predetermined pressure.
For example, as disclosed in Japanese Unexamined Patent Publication JP-A-11-200990, ordinarily the electromagnetic valve is constantly closed when a control signal to the electromagnetic valve does not exist in general. The electromagnetic valve is opened in response to a valve-opening signal, received from the control means to relieve the pressurized fuel inside the pressurization chamber on a side of low pressure. The control means further detects the fuel pressure inside the delivery pipe and opens the electromagnetic valve by applying the valve-opening signal in response to a variation of the fuel pressure. Because the fuel pressure inside the delivery pipe is increased in the discharge stroke of the fuel pump, a width of the signal is determined so that the valve-opening signal is applied in a middle of the discharge stroke and the electromagnetic valve is closed when the discharge stroke is completed.
FIG. 4 explains strokes of the fuel pump used in the conventional variable delivery fuel supply device and operating timing of the electromagnetic valve, wherein such a structure is disclosed in, for example, Japanese Unexamined Patent Publication JP-A-11-200990. An amount of piston lift in FIG. 4 is a moving distance of the plunger reciprocating by being driven by a driving cam of the internal combustion engine. A pressurizing stroke is from a bottom dead point to a top dead point. The fuel of a quantity corresponding to in this stroke is pressurized, and sent to the delivery pipes from the pressurization chamber. Further, a stroke from the top dead point to the bottom dead point is an intake stroke, in which the fuel is introduced from the fuel tank into the pressurization chamber.
Strokes A through D in FIG. 4 respectively correspond to each period of strokes in the plunger respectively of the fuel pumps, in which characteristics of the strokes are sampled and shown. Based on FIG. 4, the strokes of the conventional fuel pump and the operation of the conventional electromagnetic valve will be described. The stroke A is a case that only 50% of the total discharge quantity from the fuel pump is discharged, wherein the electromagnetic valve is opened upon receipt of the valve-opening signal at a position of 50% of the discharge stroke of the plunger, and the valve-opening signal is terminated along with completion of the discharge stroke, namely at the top dead point of the plunger, to close the electromagnetic valve. The stroke B is a case that the valve-opening signal is applied when the discharge quantity is 75%, wherein the valve-opening signal is terminated along with the completion of the discharge stroke in a similar manner to that in the stroke A.
The stroke C corresponds to a high-rate low-load in the combustion engine, for example, a case that the discharge amount from the fuel pump is large and a fuel consumption is small such as a state of using an engine brake, wherein the fuel pressure inside the delivery pipe is maintained to a predetermined value. Therefore, the discharge quantity from the fuel pump is 0%, and an amount of relief of the electromagnetic valve is 100%, whereby the valve-opening signal is applied during periods of all strokes of the plunger. The stroke D corresponds to a case that the discharge quantity from the fuel pump is small and the fuel consumption is large, for example, a low-rate large-load of the combustion engine, wherein the valve-opening signal is not applied because the discharge quantity is 100%.
A state that the discharge quantity is 0% or 100% does not highly frequently occur in these strokes. Under an ordinary state, the valve-opening signal is applied on the way of the pressurizing stroke in the plunger and finished at the top dead point. The width of the valve-opening signal is determined by the fuel pressure inside the delivery pipes. Therefore, the width of the signal constantly varies depending on the number of the revolution of the combustion engine and a state of the load for the combustion engine. Further, the width of the valve-opening signal changes in each of the strokes of the plunger even though the number of revolution and the load are constant. The control means operates the valve-opening time and the width of the valve-opening signal in each of the strokes and provides results to the electromagnetic valve.
Although, in the conventional variable delivery fuel supply device, the above-mentioned valve-opening signal is applied to the electromagnetic valve, in cases that a rise-up time of the fuel pressure inside the delivery pipe to a predetermined pressure is relatively large, for example, just after starting the combustion engine, and the fuel consumption is relatively large in comparison with the discharge quantity from the fuel pump, a time that the fuel pressure reaches the predetermined value may become very short just before the plunger passes through the top dead point, wherein the valve-opening signal becomes a pulse signal for a short time.
Meanwhile, because responsiveness of the electromagnetic valve to the valve-opening signal is limited, the electromagnetic valve can not follow the short-time pulse signal, whereby there is a case that the control becomes impossible and the fuel pressure in the delivery pipe becomes unstable. Especially, when the combustion engine is operated at a high revolution number, a time required for strokes in the plunger is shortened, and therefore the signal width of the valve-opening signal is shortened, whereby the responsiveness of the electromagnetic valve limits a maximum revolution rate of the fuel pump.
Further, because the control unit is suffered from dispersion in its control, the valve is occasionally closed in the discharge stroke before the top dead point of the plunger in the conventional control method, whereby there is a problem that the fuel pressure inside the delivery pipe becomes higher than the predetermined value by repeated discharges from the fuel pump. Further, under the high-rate small-load condition, for example, in using the compression brake in the combustion engine, there is a case the fuel consumption is sufficiently small with respect to the discharge quantity from the fuel pump, and therefore the discharge quantity is maintained to be 0%. In this case, an electric current to a coil of the electromagnetic valve becomes 100%. Because a resistance of the coil is set small to improve the responsiveness of the electromagnetic valve, there is a problem that a temperature of the coil is abnormally increased. In order to suppress the temperature increment, it is necessary to increase the resistance of the coil of the electromagnetic valve, whereby the responsiveness of the electromagnetic valve is further spoiled.